Rocks and Roles


Stratification is the process by which rock forms or deposits in layers.  This happens in sedimentary rocks and some igneous rocks.

Stratification in Rocks

Igneous rocks are rocks formed through the cooling and solidification of lava or magma.

Sedimentary rocks are rocks formed by the deposition of rocks at the Earth's surface and within bodies of water. These mineral and organic materials settle and accumulate to become layers of sedimentary rocks.

Metamorphic rocks arise from the transformation of existing rock types. They are subjected to heat temperatures that are greater than 150-200 degrees Celsius and 1500 bars of pressure, causing profound physical or chemical changes.

The age of landforms can be estimated by studying the number and thickness of rock layers.  Usually, the more rock layers there are, the older the rock is because more sediment has formed into rock layers over time.  If you dated one fossil in one area, and the same fossil in another area, the soil is most likely from the same time period.  This can also help you judge the age of the landform.

The Rock Cycle

Tectonic plates could have caused huge blocks of sedimentary horizontal to be tipped.  Older rock layers could be on top of younger rock layers if a volcano shot up the old rocks up onto the younger rock layers.

Living organisms have shaped many landforms.  Coral islands are formed from coral detritus and similar organic materials.  They are typically part of coral reefs, which cover much more area under the sea.  Limestone deposits are formed when living ocean animals die, or their shells pile up on the ocean floor.  Over millions of years, compaction and cementation can change thick sediment into limestone.  Coal forms from the remains of swamp plants buried in water.  As layer and layer of plant remains build up, the weight of the layers squeezes the decaying plants together.  Over millions of years, they slowly change into coal.  This same process happens with marine organisms to form oil deposits.

                                                 The Rock Cycle Video